Radial JDI Passive Direct Box User Guide

Warranty Information

RADIAL ENGINEERING LTD. ("Radial") warrants this product to be free from defects in material and workmanship and will remedy any such defects free of charge according to the terms of this warranty. Radial will repair or replace (at its option) any defective component(s) of this product (excluding finish and wear and tear on components under normal use) for a period of three (3) years from the original date of purchase. In the event that a particular product is no longer available, Radial reserves the right to replace the product with a similar product of equal or greater value. To make a request or claim under this limited warranty, the product must be returned prepaid in the original shipping container (or equivalent) to Radial or to an authorized Radial repair center and you must assume the risk of loss or damage. A copy of the original invoice showing date of purchase and the dealer name must accompany any request for work to be performed under this transferable warranty. This limited warranty shall not apply if the product has been damaged due to abuse, misuse, misapplication, accident or as a result of service or modification by any other than an authorized Radial repair center.

THERE ARE NO EXPRESSED WARRANTIES OTHER THAN THOSE ON THE FACE HEREOF AND DESCRIBED ABOVE. NO WARRANTIES WHETHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO, ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE SHALL EXTEND BEYOND THE RESPECTIVE WARRANTY PERIOD DESCRIBED ABOVE OF THREE YEARS. RADIAL SHALL NOT BE RESPONSIBLE OR LIABLE FOR ANY SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES OR LOSS ARISING FROM THE USE OF THIS PRODUCT. THIS WARRANTY GIVES YOU SPECIFIC LEGAL RIGHTS, AND YOU MAY ALSO HAVE OTHER RIGHTS, WHICH MAY VARY DEPENDING ON WHERE YOU LIVE AND WHERE THE PRODUCT WAS PURCHASED.

Contact: Radial Engineering Ltd., 1588 Kebet Way, Port Coquitlam BC V3C 5M5, tel: 604-942-1001, fax: 604-942-1010, email: info@radialeng.com, web: www.radialeng.com

Introduction

Congratulations on your purchase of the world's finest direct box! The Radial JDI is the latest version of the highly acclaimed JDI and is without a doubt the finest passive direct box available today. The JDI is very unique in that it does not color or alter the sound in any way. This ensures that natural tone and harmonic balance is retained, bringing out the very essence of the instrument.

The JDI employs a Jensen JT-DBE transformer for unmatched audio performance, exceptional noise rejection and high signal handling. This makes it ideal for acoustic guitar, bass and keyboards. In fact, just about any audio signal is transformed gracefully without artifact.

We suggest that you read this manual before using the JDI so that you can maximize its potential. Please log onto the Radial Engineering website at www.radialeng.com for further details and FAQ updates. We invite you to forward any comments, questions or suggestions to info@radialeng.com - we'd love to hear from you.

Enjoy!

JDI Feature Set

Key Features:

• 15dB PAD switch: Reduces input voltage for clean, distortion-free signal.
• MERGE switch: Combines left and right inputs to a mono output.
• INPUT (1/4" jack): 130k Ohm instrument input.
• THRU (1/4" jack): Thru-put to send signal to an instrument amplifier.
• Protective bookend cover: Protects switches and connectors.
• Welded I-beam construction: For strength and durability with baked enamel finish.
• Full bottom no-slip pad: Reduces slipping and provides isolation.
• Double sided PC board: Military grade with full ground plane for noise protection.
• XLR output connector: Balanced 150 Ohm mic level signal (AES standard).
• POLARITY switch: 180° polarity reverse for interfacing or phase correction.
• GROUND switch: Lifts XLR pin-1 ground to eliminate hum and noise from ground loops.
• SPEAKER switch: Pad circuit with band-pass filter for tapping speaker cabinet signals (use with load).

JDI Quick Start

This section is for advanced users — it provides a quick set of instructions for those that are familiar with direct boxes and gets right down to action! We suggest that you read through the entire manual for a better understanding of your JDI.

Caution! When connecting or disconnecting any audio device always ensure the power is off or all levels are set to zero. This practice will reduce the opportunity for any noise such as a capacitor discharge from being sent through the amplifier to the speakers, which could cause a big bang in your sound system or even cause a speaker to blow. This is especially true with phantom powered equipment.

The Radial JDI is a passive direct box and as such does not require any external power such as phantom or batteries to make it work. Just plug-in and play!

To start, make sure all switches are in the outward position. Plug the instrument into the INPUT. Connect the THRU to the guitar amplifier or keyboard mixer and the XLR OUTPUT to the PA or mixing console. Set the PAD to 0dB. Slowly turn up the input level at the mixer and listen. See the Part 5 'Features and Functions' section about the MERGE function.

The JDI's Jensen audio transformer should be able to handle most instrument signal levels without distortion. At exceptionally high signal levels, the -15dB pad should be used to reduce the input level to the transformer. If you hear distortion, simply depress the -15dB pad button. If you intend to use the JDI in parallel with a speaker load, it is important that you read the details on this application in the 'Part 5 - Features and Functions' section of this manual.

Since the Radial JDI employs an audio transformer, you are actually isolating the electrical connections between the input and output. This will usually eliminate all buzz and hum caused by so called ground loops. The JDI is designed to be grounded at either the input or the output side of the transformer. If you encounter 60-cycle hum or noise, lift the ground at the XLR output. This will assume the JDI is deriving its ground at the input from the instrument or instrument amplifier.

The JDI also features a polarity reverse. This reverses pin-2 and pin-3 at the XLR. The JDI follows the "pin-2 hot" AES standard; reversing the polarity is generally not required unless the instrument is being both DI'd and mic'd. The polarity reverse switch would allow both the mic and the JDI to be set 'in phase' should these be reversed.

You are ready to go! Now... close your eyes and listen. The JDI is without a doubt, one of the most musical DI boxes ever manufactured.

Direct Box Basics

What is a direct box anyway? The name 'direct box' comes from 'direct insertion box'. This is why these marvelous contraptions are also called DI's. 'Direct Insertion' means exactly that: To insert a signal directly or take an audio signal from the source and send it directly to a mix point or recorder. Radial designs its direct boxes to reproduce the most accurate 'picture' of the source no matter what the instrument.

Direct boxes perform the important function of impedance matching and signal balancing. They take the high impedance output from a guitar or keyboard and 'transform' it to the low impedance signal used in a balanced sound system. Balanced signals inherently cancel noise and due to their lower impedance, can travel much further without degradation. Balanced signals are the norm in professional recording, broadcast, and live sound. Properly matching the impedance provides better sound, less noise, and an extended frequency response.

Frequently Asked Questions (FAQ)

Q: What is the difference between active & passive?

A: Active DI's have a built-in pre-amp that requires battery or 48V phantom power, while passive DI's use a transformer to convert the signal and require no power supply. Both convert the instrument's high-impedance output to a low impedance balanced microphone level, allowing long cable runs without unwanted noise. Passive boxes offer transformer isolation, which can reduce ground hum and noise.

Q: Which is better – active or passive?

A: Both have their place. Passive DI's are often easier to use as they don't require power, while active DI's tend to have more reach. Passive direct boxes are generally preferred for electrically powered devices like keyboards and electronic drums.

Q: Why do people use passive direct boxes?

A: Passive direct boxes are chosen for their 'plug & play' ease of use. When equipped with a high-quality transformer, they can handle exceptionally high signal levels without harmonic distortion and process the signal without artifacts like phase distortion. Crucially, passive DI's eliminate ground loops!

Q: Why do people use active direct boxes?

A: Active DI boxes are popular for two main reasons. Firstly, high-quality transformers like Jensen's are expensive, making active DI's more cost-effective to manufacture. Secondly, in the past, instruments often used passive pickups with very low output levels. Inefficient passive DI transformers could 'load' down the pickup, altering the sound. Active (buffered or amplified) direct boxes with high input impedance solved this loading issue.

Q: Can you explain impedance loading?

A: Years ago, instruments used passive, low output pickups. These pickups 'see' the connected device (like an amplifier input) as a load they must drive. Connecting passive instruments to both a direct box and an amplifier caused the sound to change because the signal was split between two impedance loads. The amplifier presented one load, and the DI's transformer added another, reducing the signal level to the amplifier and altering the sound compared to a direct instrument-to-amp connection.

Q: What is phantom power and will it harm my JDI?

A: Phantom power is a DC supply from a mixing console, typically 48 volts and about 5mA, designed for condenser microphones. It will not harm the JDI.

Q: What is phase distortion?

A: Phase distortion affects the time-base relationship of frequencies, potentially causing instruments to get lost in a mix or bass to sound muddy. It's most noticeable at low frequencies. While many DIs perform well at 1kHz, performance can degrade at lower frequencies. The Radial JDI is tested to have less than 4° phase distortion at 20Hz, ensuring accurate time-domain response.

Q: What is the difference between phase and polarity?

A: Polarity refers to switching the (+) and (-) wires in an electrical connection. Phase distortion relates to the time domain; a 180° delay can cause cancellation. Reversing the polarity of one of two speakers has the same audible effect as a phase shift.

Q: If my JDI ever fails, what do I do?

A: The JDI is highly reliable. For repairs, contact Radial to obtain a return authorization number. It's advisable to check with your dealer first, as bad cables are often the cause of perceived issues.

Q: What is the warranty on the JDI?

A: The JDI carries a 3-year warranty, and the Jensen transformer inside has a 20-year warranty. Transformer repairs can be handled by Radial or directly with Jensen Transformers.

Q: Can I rack-mount the Radial JDI?

A: Yes, using the Radial J-Rak, a 2RU shelf that holds up to eight Radial small format direct boxes like the JDI or J48. Units can be front or rear-mounted.

Q: Can I rack-mount the Duplex?

A: No. The Radial JDI Duplex is a stand-alone device. For a rackmount solution, consider the 1-RU Radial JD6, which offers 6 JDI channels.

Specifications

Block Diagram and Connections

JDI Block Diagram: The diagram illustrates the signal path from the INPUT (1/4") through switches (PAD, MERGE, SPEAKER, PHASE, REV), the TRANSFORMER, and to the XLR OUT. A THRU (1/4") output is also shown.

Connection Examples:

• Fig. A (Instrument Amplifier Use): Instrument connects to INPUT. THRU jack connects to amplifier input. XLR OUTPUT connects to mixer.
• Fig. B (Direct to Audio System): Instrument connects to INPUT. XLR OUTPUT connects to mixer. THRU jack is unused.

Other Uses

Re-amplifying a Signal:

The JDI can be used in reverse to convert a low-impedance mic level signal back to a high-impedance guitar signal for re-amping. Connect a recorder output to a mixer, the mixer output to the JDI's XLR input (using an adapter), and the JDI's 1/4" input to a guitar amplifier. Ensure signal levels are kept low to avoid overloading the transformer.

Important Considerations

Ground Loops: The JDI's transformer provides isolation to eliminate ground loops. The GROUND switch lifts the XLR pin-1 ground to help resolve severe hum or noise issues. If using the THRU jack, ensure the amplifier is grounded. If not using the THRU, the JDI should be grounded via the XLR output.

Speaker Connection: The JDI can tap signals from a speaker cabinet using the SPEAKER switch. IMPORTANT: The JDI is NOT a load box. An amplifier MUST be connected to its speaker load first. Depress both the -15dB PAD and SPEAKER switches for this function. The SPEAKER switch also engages a band-pass filter.

Input Levels: While the JDI handles high signal levels, extremely high outputs (e.g., from CD players or headphone outs) may require the -15dB PAD switch to prevent distortion.

Phase and Polarity: The POLARITY switch reverses pin-2 and pin-3 on the XLR output. This can correct phase issues when combining signals (e.g., mic and DI) or interface with older equipment.

About Radial Engineering

Radial Engineering Ltd. is dedicated to producing high-quality, reliable audio equipment. Their products are known for their robust construction, innovative features, and exceptional audio performance, making them a staple in professional studios and live sound environments worldwide.